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A248023 Even numbers which are neither primes nor perfect powers and are coprime to the sum of their divisors. 1
50, 98, 242, 338, 392, 578, 722, 800, 968, 1058, 1250, 1352, 1682, 1922, 2312, 2450, 2738, 2888, 3362, 3698, 3872, 4232, 4418, 4802, 5408, 5618, 6050, 6272, 6728, 6962, 7442, 7688, 8450, 8978, 9248, 10082, 10658, 10952, 11552, 12482, 12800, 13448, 13778, 14450 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1500

EXAMPLE

50 is in the sequence since it is neither a prime nor a powerful number and its divisors 1, 2, 5, 10, 25, and 50 sum to 93, which is coprime to 50.

MATHEMATICA

perfectPowerQ[n_] := n == 1 || GCD @@ FactorInteger[n][[All, 2]] > 1; Select[ 2 Range@ 7500, !PrimeQ[ #] && GCD[#, DivisorSigma[1, #]] == 1 && !perfectPowerQ[ #] &]

PROG

(PARI) lista(nn) = {forstep(n=4, nn, 2, if (!ispower(n) && (gcd(n, sigma(n))==1), print1(n, ", ")); ); } \\ Michel Marcus, Oct 02 2014

CROSSREFS

Cf. A003624, A106543, A248020.

Sequence in context: A260901 A090997 A141757 * A328253 A044139 A044520

Adjacent sequences:  A248020 A248021 A248022 * A248024 A248025 A248026

KEYWORD

nonn,easy

AUTHOR

Robert G. Wilson v, Sep 29 2014

STATUS

approved

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Last modified August 9 21:08 EDT 2022. Contains 356026 sequences. (Running on oeis4.)